1. Field of the Invention
The present invention relates to a fluid dynamic bearing used in an electric motor, an electric motor, and a recording disk drive apparatus including the electric motor with the fluid dynamic bearing.
2. Description of the Related Art
A fluid dynamic bearing is used in many small-sized spindle motors for recording disk drive apparatuses or the like. In such a fluid dynamic bearing, a shaft is supported by a sleeve via lubricating oil, whereby noise reduction is achieved.
JP-A 2005-155912 discloses a technique for causing the lubricating oil used in the fluid dynamic bearing to sequentially flow along an inner circumferential surface, a lower surface, an outer circumferential surface, and an upper surface of a sleeve. In addition, an inner tapered seal portion is provided between a cover member placed above the sleeve and an outer circumferential surface of a shaft, while an outer tapered seal portion is provided between a sleeve housing covering the outer circumferential surface of the sleeve and an outer circumferential surface of the cover member.
In a bearing mechanism as described in JP-A 2005-155912, the lubricating oil is retained by the tapered seal portions at two locations. However, a large resistance in a channel between these tapered seal portions might lead to an excessive rise of a liquid/gas interface in the outer tapered seal portion, resulting in overflow of the lubricating oil, or an excessive lowering of a liquid/gas interface in the inner tapered seal portion, resulting in depletion of the lubricating oil.